In general, sludge and all the residues but not organic materials, which are generated in filtration plants or sewage treatment plants, factories or incinerating facilities and the like, are classified as wastes and are disposed of by a specified method through a collection process. However, collection and disposal of such waste sludge requires a large-sized collection facility and a collection plant to be installed. In addition, the waste sludge collected is not buried and disposed of as it is, but is buried in a state in which the waste sludge is mixed with clay picked to obtain natural regeneration in an environmental aspect. For this reason, the amount of clay consumed as well as the volume of the waste sludge and the amount of waste sludge buried due to mixed clay are increased excessively, which makes it difficult to designate and establish a waste dump.
In the process of disposing of waste sludge, excessive waste disposal cost is spent, and because the designed waste dump must not have an effect on soil or environment of adjoining areas, pre-treatment and post-management are very strictly carried out, leading to a significant increase in expense.
In addition, natural construction materials become increasingly deficient along with the development of the industrial society. In this context, there has been proposed a method which manufactures lightweight aggregate as a construction material, which comprises: mixing sludge waste with an inorganic material; forming the mixture into a desirably shaped body; and drying and calcining the shaped body to obtain a construction material. The lightweight aggregate thus manufactured has an advantage in which the specific gravity of concrete used can be reduced as well as soundproof and thermal insulation can be obtained simultaneously.
For example, in Korean Patent Registration No. 10-0859002, there has been proposed a method of manufacturing artificial lightweight aggregate using sewage sludge, which comprises: grinding sewage sludge, coal fly ash, and clay into small particles having a size of less than 1 mm; forming the mixture into a shaped body; calcining the shaped body at 1100° C. to 1200° C. for 10 to 15 minutes to obtain the lightweight aggregate. Further, in Korean Patent Registration No. 10-0450898, there has been proposed a method of manufacturing calcined construction materials using sewage sludge, which comprises: primarily drying and grinding sewage sludge in a dehydrated cake state for 24 hours; mixing the ground sewage sludge with clay, silica sand, plaster, and blast furnace slag powder, forming the mixture into a shaped body, and secondarily drying the shaped body; and calcining the dried body at 900° C. to 1100° C. for 13 hours to obtain the construction materials. As such, many patents have proposed various methods. The inventions of the above patents have an effect in that lightweight aggregate can be manufactured without any leaching of heavy metals, but still entails a problem in that much energy is consumed in the course of manufacturing the construction materials, diversification of products is difficult, and the strength is weak in case of a product manufactured using the residues generated after incineration.
Accordingly, the present inventors have made extensive efforts to solve the above-described problems occurring in the prior art and, as a result, have found that lightweight construction material having excellent physical properties can be manufactured through a simplified process by adding feldspar, bentonite, zeolite, loess, mica and agalmatolite to sludge waste, thereby completing the present invention.